Using weather data with moisture content instead of HREL

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DavidG
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Using weather data with moisture content instead of HREL

Post by DavidG » Mon Sep 07, 2020 5:12 pm -1100

The weather file I have obtained for a specific location has moisture content (g/kg) - not relative humidity.
Is there a way to use this data?

Thomas
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Re: Using weather data with moisture content instead of HREL

Post by Thomas » Mon Sep 07, 2020 10:10 pm -1100

Hi DavidG,

yes, if you also know the temperature and the barometric pressure you can convert those data to relative humidity.

The formulas are given in our Air Humidity Tutorial. If your data have units kg/kg or g/kg, they are either the mixing ratio or the specific humidity. Ideally, you should know which of them, but for normal atmospheric humidities the difference is small and you can use either formula. Solve the relevant formula for the partial pressure p and use p to calculate the relative humidity.

If you don't know the barometric pressure, a rough estimate will do. For a location at height h above sea level you can estimate the average pressure in Pascals as P = 101325 * exp(-1.2*10^-4 * h).

Regards,
Thomas

DavidG
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Re: Using weather data with moisture content instead of HREL

Post by DavidG » Thu Sep 10, 2020 8:45 pm -1100

Hi Thomas

The data (from Australian Bureau of Meteorology) includes atmospheric pressure and dry bulb temperature so I will work on the calculations you suggest.

Thanks

David

Thomas
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Re: Using weather data with moisture content instead of HREL

Post by Thomas » Fri Sep 11, 2020 2:51 am -1100

So it's all the better :D And please keep in mind that the pressure at station height is required, not the pressure at sea level.

Regards,
Thomas

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